What is the concept of how many millimeters of SLR lens? How far is 50 mm suitable for shooting? 100 mm? What about 500 mm? How to calculate?

Focal length refers to the distance from the center of the lens to the focal point, usually in millimeters. The camera lens projects the light in the shooting scene onto the film or sensor. The visible field of view (FOV) is determined by the horizontal and vertical distances of the scene covered by the lens.

Large sensors and films have larger FOV and can record more information in the scene. The focal length and FOV are usually based on 35mm film, because this format (35mm) is commonly used.

In 35mm photography, a lens with a focal length of 50mm is called a "standard lens" because the shooting scene is neither enlarged nor reduced, and the shooting range is the same as that seen by the naked eye (the image angle is 46).

Wide-angle lens (short focal length) can make the camera "see wider" because its imaging angle is larger; The telephoto lens (long focal length) can make the camera "see farther", but the visual range is narrower. The following are descriptions of focal lengths corresponding to some typical lenses:

The focal length of 35mm format corresponds to the lens type.

& lt20

fish-eye lens

24 mm to 35 mm

wide-angle lens

50 mm

standard lens

80 mm to 300 mm

long shot

& gt300 mm

Super telephoto lens

By adjusting the focal length, the photographer can choose to shoot at a shorter distance or a longer distance to get different perspective feelings. Some digital cameras will have barrel distortion at the wide-angle end and pin pad distortion at the telephoto end.

35mm equivalent focal length

Because the sensor of digital camera is smaller than the area of 35mm film, digital camera engineers introduced the concept of "equivalent focal length" to convert the focal length of digital camera lens into an equivalent focal length of 35mm, which is convenient for photographers to study.

Optical zoom and digital zoom

Optical zoom = maximum focal length value/minimum focal length value

For example, the focal length of an optical zoom lens is 28-280mm, and its optical zoom multiple is 280mm/28mm, that is, 10 times. This means that the size of the object at the telephoto end (280mm) is 10 times that at the wide-angle end (28mm). Optical zoom should not be confused with digital zoom.

Extended data:

Early cameras used a single-lens lens, and the imaging could be sharper than pinhole, and the aperture was larger, which could basically be photographed by hand. The working aperture is about f/ 12. Because it was a large negative, the effect was acceptable.

From two lenses to three lenses, the aperture of the lens is larger and the imaging is quite sharp. Cook triplets are the best design known at present. If it is a four-lens, the imaging is quite good, such as Zeiss Tessar.

The four-piece set has three groups of structures, in which two pieces are glued together to form a group. The only problem with the four-piece sky-inserted lens is that the aperture can't be made too large, otherwise the image quality will be degraded. For a 35mm camera, the ceiling of the ceiling structure is f/2.8, even if the best optical glass is used at present. If you want a larger aperture, you need more lenses.

Speed (that is, the maximum aperture) is not the only problem. The larger the viewing angle, the more lenses are needed. A low-speed small-angle lens, such as Leitz 560mm f/6.8 Telyt, uses only two lenses. Generally, 50mm f/ 1.4 needs 6 or 7 tablets, and 2 1mm f/4.5 Zeiss Biogon needs 8 tablets. More lenses make them bigger, heavier and more expensive.

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